The present invention relates to a packet routing apparatus and a packet routing method. More particularly, this invention relates to the packet routing apparatus and packet routing method incorporating an extended function module, such as a router, a LAN switch, and the like. A bridge is an apparatus for connecting a plurality of networks, mutually connecting at a data link layer of a network system hierarchy, and controlling the relay according to an MAC address in the packet. A router connects at a network layer, which is the upper layer of the data link layer, and carries out relay according to an IP address in the packet.
For example, U.S. Pat. No. 5,434,863 (corresponding Japanese Patent Publication Laid-Open Patent Application No. 10 5-199230) discloses a router.
FIG. 18 shows a block diagram of the router disclosed in the above application. This router comprises a main processing module 2, routing modules 31 to 3n, an upper BUS 1, lower BUS 41 to lower BUS 4n, and line control modules 51 to 5n. The router controls protocols, the number of protocols matching the number of network layers. The routing flow of the router will be explained using an IP (Internet Protocol) protocol as a representative example.
When a packet is received from a communication line, the port control module 51 sends the packet via the lower BUS 41 to the routing module 31. The routing module 31 retrieves route information, held by itself, based on the IP address in the received packet, selects a predetermined route or an optimum route, and selects for example, the routing module 32. The routing module 31 relays the received packet via the upper BUS 1 to the selected routing module 32. The routing module 32 extracts the packet from the upper BUS 1, and sends it via the lower BUS 42 to the port control module 52. The packet is transmitted from the port control module 52 to the destination communication line. Conversely, when transmitting the packet from the port control module 52 to the port control module 51, the packet is routed along a route which is the reverse of that described above.
The patent application mentioned above discloses one example of a supplementary processor for executing various functions in a router of this type. In this example, the supplementary processor for supplementing the functions of the main processing module is connected to the upper BUS.